The present invention relates to bridge cranes, and particularly to a control unit requiring only one hand of an operator to be used to control the direction and speed of traversing movement of the hoist portion of such a bridge crane.
A bridge crane includes a pair of elevated parallel rails extending longitudinally along opposite sides of an area within which the bridge crane is designed to lift, carry, and lower loads. A bridge extends horizontally between the longitudinal rails and is movable along the rails, usually by electrically powered motors. A hoist is located on a hoist carriage which may be moved along the bridge, between the longitudinal rails of the bridge crane. A motor is usually provided for moving the hoist carriage along the bridge, and the hoist also includes a motor for raising and lowering suspended loads.
Previously known bridge crane control units are typically suspended on flexible pendant cables whose upper ends are attached to the hoist carriage. Usually several push-button switches are provided on such pendant control units, with each push-button controlling operation of a part of the bridge crane in a single direction. Thus, there are usually at least six push-buttons located on such a pendant control unit. While such push-button switches are normally labeled, the labels may be missing or worn away. The labels provided may be somewhat confusing, as well, since terms such as "forward" or "reverse" often do not give a clear indication of which direction the hoist carriage or bridge is going to move when that particular switch is closed. As a result, operators must become familiar with each particular bridge crane installation, and mistakes are likely to occur.
It is frequently desirable to save time by moving a load suspended from a bridge crane in a diagonal traversing direction. This can be accomplished using the previously known pendant control unit only by simultaneously pushing two buttons, to move the bridge along the rails and to move the hoist carriage along the bridge simultaneously. Since operating two push-buttons simultaneously normally requires the use of both hands, an operator is unable to move a load diagonally and also hold the load with one hand to steady it while it is being moved by the bridge crane.
While some attempts have been made to improve upon the conventional pendant control units for bridge crane, these have not been entirely satisfactory. For example, Somborn et al., U.S. Pat. No. 4,209,681 discloses a control unit which improves upon the conventional pendant control unit by providing switches arranged to be easily visible and to be comfortable for the operator's hand, but there are still an inconveniently large number of switches contained in the Somborn et al., unit.
Raetz U.S. Pat. No. 3,931,486 includes an easily gripped control handle for a hoist. A single rocker switch is located conveniently for operation by the operator's thumb, but this control unit does not provide any control over the direction of traversing movement of a bridge crane. Instead the thumb-operated lever controls merely the speed of operation of a hoist motor.
Cordes U.S. Pat. No. 3,755,725 provides a pistol grip connected by a rod to the hook of a hoist to control manually the lateral movement of a load being lifted or lowered. A rocker switch is provided in the pistol grip to control raising and lowering operation of the hoist. Alternatively, push buttons may be provided on the rear side of the pistol grip for controlling operation of the hoist motor. The Cordes device does not provide for control of motors to move the hoist mechanism laterally or longitudinally.
None of the above-identified devices, however, deals with control of the direction of traversing movement of a bridge crane hoist in a way which makes it possible to control such a bridge crane using only one of an operator's hands.
What is needed, therefore, is a control unit which provides for safe control of the direction of traversing movement of a hoist assembly, as well as control over the raising and lowering operation of the hoist, which provides for diagonal, as well as straight lateral traversing movement of the hoist carriage along the bridge or longitudinal movement of the bridge along the rails of a bridge crane, and which requires the use of only one hand by the crane operator.